Stacker/autoloader systems are becoming more and more important for companies having a need for very large data storage capacities at a low cost. Different types of stacker/autoloader systems are made to fit requirements of different media types, such as 1/4" and 1/2" tape cartridges, 4 mm and 8 mm tape cassettes and writable optical tapes or disks.
A typical stacker/autoloader system has a single tape drive and a single magazine. A specially designed magazine containing the tape cassettes or cartridges may be placed in a magazine holder of the stacker/autoloader system. Many systems include a door covering the magazine after it is loaded. Often this door can be physically locked either mechanically or electrically to prevent injuring an operator while the magazine is moving.
The stacker/autoloader system, based on commands from a connected host, sends signals to a mechanical magazine positioning system to move the magazine to a specific position such that a particular cassette is in front of the tape drive. Signals will then be issued to a loading mechanism to activate a cassette load operation which will load the cassette into the tape drive. The tape drive may then be activated to perform one or more read or write operations.
At the end of the operations, the system initiates an unload operation placing the cassette back into the magazine. The control unit may then move the magazine to a new position to enable the loading of another cassette and so on. Although some systems may only operate with the cassettes in the magazine in a sequential order, i.e. cassette 1 first, then cassette 2, then cassette 3 and so on, systems may be designed such that cassettes or cartridges may be randomly selected for loading/unloading.
At the end of a complete magazine operation, the operator may open the stacker/autoloader door and take out the magazine and store it for later use. The operator may then install another magazine, and the host may continue its operation on the stacker/autoloader system.
Compared to a single drive, a stacker/autoloader makes it possible to increase total capacity with a typical factor in a range of four to sixteen times for a stacker and from fifty and upwards for an autoloader. This is achieved at a low total system cost. The user may have many magazines loaded with tape cartridges, and the stacker/autoloader may, therefore, act as an efficient, low-cost library system.
However, having many magazines available also increases the risk of the operator loading an incorrect magazine, The host will normally be able to detect the use of an incorrect magazine by reading the contents of one or more of the cassettes/cartridges, but this is a time-consuming operation which slows down the performance of the total system.